Well, two things:
1) Will fix the immediate problem. You declare
con
, but you never give it a value! At some point you need to set con to an instance of an SqlConnection, so replace this:
con.ConnectionString = "Data Source=SuperComp-PC;Initial Catalog=Testdb;Integrated Security=True"
With this:
con = New SqlConnection("Data Source=SuperComp-PC;Initial Catalog=Testdb;Integrated Security=True")
2) Do not concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead.